Electrochemically regenerated liquid desiccant dehumidification system using a secondary heat pump

ABSTRACT

A liquid desiccant regenerator configured to produce a first output stream with a higher concentration of a liquid desiccant than a first input stream. The regenerator also produces a second output stream with a lower concentration of the liquid desiccant than a second input stream. Regeneration of the liquid desiccant in the liquid desiccant regenerator decreases a temperature of the liquid desiccant regenerator. The system includes an air contactor coupled to the first output stream and exposing an input air stream to the first output stream. The first output stream absorbs water from the input air stream to form at least one diluted output desiccant stream. A heat pump of the system is thermally coupled to move the heat from the first output stream to the liquid desiccant regenerator. The heat moved to the liquid desiccant regenerator increases an efficiency of the liquid desiccant regenerator.

TECHNICAL FIELD

This disclosure relates generally to systems that utilizeelectrochemical regeneration of a liquid desiccant.

SUMMARY

Embodiments described herein are directed to a heat pump system using anelectrodialysis apparatus. In one embodiment, a system includes a liquiddesiccant regenerator configured to produce a first output stream from afirst input stream. The first output stream has a higher concentrationof a liquid desiccant than the first input stream. The regenerator alsoproduces a second output stream from a second input stream. The secondoutput stream has a lower concentration of the liquid desiccant than thesecond input stream. Regeneration of the liquid desiccant in the liquiddesiccant regenerator decreases a temperature of the liquid desiccantregenerator. The system includes an air contactor coupled to the firstoutput stream and exposing an input air stream to the first outputstream. The first output stream absorbs water from the input air streamto form at least one diluted output desiccant stream. The at least onediluted output desiccant stream is circulated back into the liquiddesiccant regenerator. A heat pump of the system is thermally coupled tomove the heat from the first output stream to the liquid desiccantregenerator. The heat moved to the liquid desiccant regeneratorincreases an efficiency of the liquid desiccant regenerator.

Other embodiments are directed to a system that includes a liquiddesiccant regenerator configured to produce a first output stream from afirst input stream. The first output stream has a higher concentrationof a liquid desiccant than the first input stream. The regenerator alsoproduces a second output stream from a second input stream. The secondoutput stream has a lower concentration of the liquid desiccant than thesecond input stream. The system includes an air contactor coupled to thefirst output stream and exposing an input air stream to the first outputstream. The first output stream absorbs water from the input air streamto form at least one diluted output desiccant stream. The at least onediluted output desiccant stream is circulated back into the liquiddesiccant regenerator. The system includes a vapor compression heat pumphaving a refrigerant loop between a condenser and an evaporator. Thesystem also includes a fluid loop between the evaporator and the aircontactor, the fluid loop thermally coupled to move the heat from theair contactor to the evaporator.

In another embodiment, a method involves producing a first output streamfrom a first input stream in a liquid desiccant regenerator, the firstoutput stream having a higher concentration of a liquid desiccant thanthe first input stream. A second output stream is produced from a secondinput stream in the liquid desiccant regenerator, the second outputstream having a lower concentration of the liquid desiccant than thesecond input stream. An input air stream is exposed to the first outputstream in an air contactor. The first output stream absorbs water fromthe input air stream to form at least one diluted output desiccantstream. The at least one diluted output desiccant stream is recirculatedback into the liquid desiccant regenerator. Heat is moved from the firstoutput stream to the liquid desiccant regenerator via a heat pump.

The above summary is not intended to describe each disclosed embodimentor every implementation of the present disclosure. The figures and thedetailed description below more particularly exemplify illustrativeembodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The discussion below refers to the following figures, wherein the samereference number may be used to identify the similar/same component inmultiple figures. However, the use of a number to refer to a componentin a given figure is not intended to limit the component in anotherfigure labeled with the same number. The figures are not necessarily toscale.

FIG. 1 is a diagram of a redox flow electrochemical regenerator stackand liquid desiccant system according to an example embodiment;

FIG. 2 is a graph showing power consumption under various conditions ofa regenerator stack and liquid desiccant system according to an exampleembodiment;

FIG. 3 is a diagram of a redox flow electrochemical regenerator stackand system according to another example embodiment;

FIGS. 4 and 5 are diagrams showing secondary heat pumps integrated intoa liquid desiccant regeneration system according to example embodiments;

FIGS. 6 and 7 are diagrams showing different arrangements of a liquiddesiccant system in a cooling system according to example embodiments;and

FIG. 8 is a flow diagram of a method in accordance with certainembodiments.

DETAILED DESCRIPTION

The present disclosure relates to electrochemically regenerated liquiddesiccant dehumidification systems. A liquid desiccant system may beused in, among other things, heating, ventilation, and air-conditioning(HVAC). Air conditioning is an energy intensive process and isresponsible for nearly 10% of U.S. electricity consumption, withdehumidification accounting for more than half of the energy load inhumid regions. The systems described herein provide an efficient,thermodynamic approach to dehumidification for air conditioningincluding a redox-assisted electrodialysis liquid desiccant regeneratorthat utilizes a heat pump.

Liquid desiccants (e.g., aqueous solutions of lithium chloride, LiCland/or other salt such as NaCl, LiBr, and CaCl₂) will absorb moisturefrom air across an air-to-liquid interface (e.g., a membrane interface),which decreases concentration of the desiccant solute, resulting in adiluted output stream of liquid desiccant. In order to regenerate theliquid desiccation system in a loop, the diluted liquid desiccants canbe efficiently re-concentrated using a redox-assisted regenerator. Thistype of regenerator, referred to as a shuttle-promoted electrolyteremoval (SUPER) cell, can increase or decrease concentrations of solutesin solutions through the use of ionic transport membranes and a redoxshuttle.

In FIG. 1 , a diagram shows a SUPER cell 100 according to an exampleembodiment. The cell 100 includes two electrodes 116, 118, at leastthree ion exchange membranes 110, 112, 114, and an energy supply 123.The first electrode 116 contacts a first solution of a firstredox-active electrolyte material and configured to have a firstreversible redox reaction with the first redox-active electrolytematerial. The second electrode 118 contacts a second solution of asecond redox-active electrolyte material and configured to have a secondreversible redox reaction with the second redox-active electrolytematerial. For purposes of simplicity, the first and second redox-activeelectrolyte solutions are shown in the FIG. 1 as a single redox shuttlesolution 117 comprising the redox-active electrolyte materials.

Examples of a redox shuttle solution include1,1′-bis((3-trimethylammonio)propyl)ferrocene ([BTMAP-Fc]²⁺) and1,1′-bis((3-trimethylammonio)propyl)ferrocenium ([BTMAP-Fc]³⁺), or1,1′-bis((3-dimethylethylammonio)propyl)ferrocene ([BDMEAP-Fc]²⁺) and1,1′-bis((3-dimethylethylammonio)propyl)ferrocenium ([BDMEAP-Fc]³⁺),which are highly stable ferrocene derivatives that have very rapidelectrochemical kinetics and negligible membrane permeability, orferrocyanide/ferricyanide ([Fe(CN)_(6]) ⁴⁻/[Fe(CN)_(6]) ³⁻). Additionaldetails for example redox shuttle solutions can be found incommonly-owned U.S. Pat. Application 17/390,600, filed Jul. 30, 2021(Attorney docket number 20210171US01/0600.382US01), which is herebyincorporated by reference in its entirety.

The redox shuttle 117 is circulated between the two electrodes 116, 118as shown by redox shuttle loop 124. When an electrical potential isapplied to each electrode 116, 118 by energy supply 123, the redoxshuttle is oxidized at a first electrode (e.g., 116) and reduced at theopposite electrode (e.g., 118). The energy supply 123 may be any varietyof direct current (DC) energy supply such as a battery, photovoltaicpanel, galvanic cell, potentiostat, AC/DC power converter, etc., and theenergy supply may be contained within the electrochemical cell 100 or beexternal and coupled to the cell 100. Thus, as the shuttle 117circulates between the electrodes, the portions of the shuttle 117 arecontinuously alternating between the redox states. In other words, theelectrical potential engenders faradaic reactions happening at the twodifferent electrodes 116, 118 and the redox material undergoing thefaradaic reactions is circulated from one electrode to the other andback again.

In certain embodiments, each electrode 116, 118 may contact separateredox-active solutions instead of the same redox shuttle solution 117being flowed in a loop. The separate redox-active solutions may have thesame redox-active electrolyte material or different redox-activeelectrolyte materials. When different redox-active solutions are usedfor the respective electrodes 116, 118, the energy supply mayperiodically reverse the potential supplied to the electrodes to restorethe state of charge (e.g., the proportion of redox-active electrolytematerial in each solution that is in the oxidized state compared to thereduced state) of each of the redox-active electrolyte materialsolutions.

Positioned between the electrodes 116, 118 are three ion exchangemembranes, which alternate in the type of ion exchanged. For example,among three membranes, a center membrane 110 may be a cation exchangemembrane flanked by second 112 and third 114 anion exchange membranes,as is shown in FIG. 1 . However, in other embodiments, the center, firstmembrane may be an anion exchange membrane and the second and thirdmembranes may be cation exchange membranes. The membranes 110, 112, 114define chambers, channels, or reservoirs, in the electrochemical cell100. As may be seen, a first membrane 110 and a second membrane 112define a first chamber 106, which in this example is configured as adesalinate chamber that decreases salt concentration in a fluid. Thefirst membrane 110, in combination with a third membrane 114, alsodefines a second chamber 108, which in this example is configured as asalinate channel that increases salt concentration in a fluid.

The membranes 110, 112, 114 are ion-selective as well aswater-permeable, are insoluble in organic solvents, and are inert (e.g.,do not chemically change) in the reaction mixture and/or products. Incertain embodiments, the membranes are reinforced with a polymer meshintegrated into the membrane itself and in other embodiments, themembranes are not reinforced. It will be understood that this can beextended to additional membranes, e.g., N membranes of alternating typethat define respective N-1 channels or reservoirs.

A first stream 102 flows through the first chamber 106 of theelectrochemical cell 100. The first stream 102 includes at least asolvent (water in this example) and a salt (LiCl in this example)dissolved in the solvent at a first salt concentration (about 35% byweight in this example) when it enters the first chamber 106. A secondstream 122 flows through the second chamber 108 of the electrochemicalcell 100. The second stream 122 has a second salt concentration (about35% by weight) as it enters the first chamber. The second saltconcentration is the same as the first salt concentration in thisexample, although could be different. During an operational mode of theelectrochemical cell 100, an electrical potential is applied to theelectrodes 116, 118 and the first and second streams 102, 122 are moved(e.g., pumped) through the first and second chambers 106, 108.

When an electrical potential is applied to the electrodes 116, 118, theredox shuttle 117 is oxidized at one electrode 116 and reduced at theother electrode 118, thereby driving salt ions 127 from the first stream102 in the first chamber 106 into the second stream 122 in the secondchamber 108. In particular, the redox shuttle 117 at the first electrode116 accepts at least one ion 134 from the catalyst in the first chamber106. The redox shuttle 117 at the second electrode 118 drives at leastone ion 133 into the second stream 122 in the second chamber 108, andthe charge is balanced by driving at least one ion 127, of opposite signof charge to ions 133, 134, from the first stream 102 in the firstchannel 106 across the center membrane 110 into the second stream 122 inthe second channel 108.

The result of the electrical potential being applied to the electrodesis that the first stream 102 has a reduced concentration of salt (e.g.,below a 1% threshold concentration) during the operation mode whenexiting the first chamber 106 and the second stream 122 increases inconcentration of salt when exiting the second chamber 108. The outputsof the first and second chambers 106, 108 can be further processed bysubsequent stages of a similar SUPER cell to achieve similar orincreased levels of desalinization and salinization. Such a system maybe used with various other salts, such as water-soluble ionic salts.Example cations that can be present in the salts include, but are notlimited to, hydronium, lithium, sodium, potassium, magnesium, calcium,aluminum, zinc, and iron. Example anions that can be present in thesalts include, but are not limited to, chloride, bromide, iodide, halideoxyanions, sulfur oxyanions, phosphorous oxyanions, and nitrogenoxyanions.

As noted above, the SUPER cell 100 can be used to regenerate a liquiddesiccant stream that flows through a liquid-to-air heat and massexchanger, including a direct contactor, packed bed air contactor, orliquid-to-air membrane energy exchanger (LAMEE) 130, which is shown inFIG. 1 coupled to the SUPER cell 100. For the purposes of thisdisclosure, instances of a a LAMEE shown in any of the embodiments maybe replaced with and/or augmented with any type of direct contact ormembrane liquid-to-air heat and mass exchanger.

As seen in FIG. 1 , the second, concentrated stream 122 is used as aninput 131 to the LAMEE 130. The LAMEE 130 receives an input air stream142 with relatively high relative humidity (RH), and water vapor in theinput air stream 142 is absorbed into the liquid desiccant. This resultsin the LAMEE 130 outputting an output air stream 144 with a relativelylow RH. The water being absorbed in the liquid desiccant results in adiluted output stream 143 from the LAMEE 130, which can be fed back intothe SUPER cell. In this case, the output of the first, diluted stream102 can be discarded or used elsewhere.

The absorption of water into the liquid desiccant results in an increasein the temperature of air 142, 144 flowing through the LAMEE 130, whichis a well-known thermodynamic phenomenon when water condenses from a gasto a liquid. This increase in temperature can be reduced or eliminatedby heat absorbing/accepting element 136 (e.g., heat exchanger) thatabsorbs heat energy 135 from the LAMEE 130. Heat can also influenceenergy consumption of the SUPER cell 100. For example, running the SUPERat higher temperatures can make its operation more efficient, e.g., bylowering the electrical resistance of the membranes/electrodes/solutionsand increasing the electrochemical kinetics. Therefore, a heatemitting/rejecting element 138 (e.g., heat exchanger) can supply heat139 to the SUPER cell 100 and/or any of its internal flows. Forinstance, applying heat to specific components or fluid streams in theSUPER can be used to induce a temperature gradient inside the SUPER toencourage favorable phenomenon (like resistance) and discourageunfavorable phenomenon (like water osmosis). In a SUPER design withmultiple stages, heat can be applied to specific stages to promotefavorable performance. Inputting heat to SUPER cell 100 can alsocompensate for the endothermic effects due to regeneration of the liquiddesiccant.

Specific subsets of components of the SUPER cell 100 can be heated viathe heat rejecting element 138 using conventional heat transferelements, such as heat conductive structures, vapor chamber heat pipes,convective transfer from heat sinks, etc. In one embodiment, heat fromelement 138 can be applied to one or more of the membranes 110, 112, 114to lower electrical resistance. In another embodiment, heat from element138 can be applied to one or more of the electrodes 116, 118 to lowerelectrical resistance. In another embodiment, the stream 143 input tothe SUPER cell 100 may be heated before or after entering the cell. Forexample, heating the concentrated stream 122 while keeping the dilutestream 102 relatively cooler can reduce water osmosis across the centermembrane 110. In other embodiments, the redox shuttle loop 124 may beheated.

The desiccant flow rate through the LAMEE 130 can also affecttemperatures and system energy consumption. A high flow rate of liquiddesiccant has low concentration change between the input stream 131 andthe output stream 143. This may require more energy to reconcentrate theinput stream 131 via the SUPER cell, as regeneration requires much moreenergy at higher concentrations. For example, the graph in FIG. 2 showsa marked increase in slope of the energy consumption curves for cellvoltages from 0.1 to 0.5 volts once LiCL desiccant concentration ishigher than 25-30% by weight. One the other hand, a high desiccant flowrate but may require less rejection of heat 135 from the LAMEE 130. Alow flow rate of liquid desiccant through the LAMEE 130 increases theconcentration change between the input stream 131 and the output stream143. This can reduce the energy needed to reconcentrate the input stream131 via the SUPER cell 100, although may increase the rejection of heat135 from the LAMEE 130.

The heat absorbing element 136 and heat emitting element 138 may bethermally coupled to a same heat pump or two different heat pumps.Generally, a heat pump is a system that utilizes a heat transfer medium(e.g., gas, liquid, or solid) to move heat in a direction opposite thatof spontaneous heat transfer. Well-known heat pump systems includevapor-compression (VC) cycle machines used in refrigerators andair-conditioning. A working fluid (e.g., refrigerant such as R-134A,R-407C, etc.) is compressed and condensed in a condenser. Thecompression and condensation cause a rise in fluid temperature whichresults in heat transfer to the outside air (OA) or other heat sink. Thecooled working fluid is sent from the condenser to an expansion valvewhere it evaporates into an evaporator. The evaporation absorbs heat andthe working fluid is sent back to the compressor to complete the cycle.This flow path of the working fluid is also referred to herein as arefrigerant loop.

Other types of heat pump systems include vapor absorption systems wherea liquid refrigerant evaporates in a low partial pressure environment,absorbing heat from its surrounding. The vapor is then absorbed inanother liquid, which is then heated to cause the refrigerant toevaporate out again. One advantage to absorption systems is that theycan be built using no moving parts, other than the refrigerant itself.Other heat pumps, such as ground source heat pumps, utilize a constanttemperature source (e.g., the earth) transfer heat to or from the groundusing a working fluid, and may not need to rely on phase changes of theworking fluid. Solids can be used as a heat pump media, such as inthermoelectric cooling devices.

The embodiments described herein improve the performance ofelectrochemically regenerated liquid desiccant dehumidifiers by use of asecondary heat pump. Generally, as the term is used herein, a primaryheat pump moves heat between a heating/cooling target (e.g., forced airin an HVAC system or a water stream) and a thermal sink (e.g., theground or atmosphere). A secondary heat pump includes additional heatexchangers in the primary heat pump path to heat or cool othercomponents in the system. Many dehumidification systems use either aprimary heat pump (as in the case of VC cycle air-conditioning) or asecondary heat pump (as in the case of a thermally regenerated desiccantwheel). The heat pump can be used to increase the relative humidity ofair by cooling it, or to cool the air after dehumidification,compensating for heating caused by the dehumidification. In someembodiments, an electrochemically regenerated liquid desiccant systemdirectly couples with the heat rejection (hot side) of the secondaryheat pump, the heat accepting (cold side) of the secondary heat pump, orboth.

Before discussing the heat pump aspects in greater detail, it will beunderstood that a liquid desiccant system as shown in FIG. 1 may employmore than one SUPER cell in order to improve efficiency. For example,changing concentration levels of the liquid desiccant solutions insmaller, discrete steps can minimize osmotic pressure differentials ineach channel of the SUPER cells. Thus, in some embodiments, a SUPERliquid desiccant regenerator has two or more stages, each subsequentstage being configured to produce an output stream having aconcentration of the liquid desiccant higher than the previous stage.

In FIG. 3 , a diagram shows how a stack 301 of two SUPER cells 300, 302can be coupled together into a two-stage regenerator to increaseefficiency in a liquid desiccant regeneration system. A LAMEE 304receives a concentrated stream 306 of liquid desiccant from the firstSUPER cell 300. The concentration level of the stream 306 is about 30%here, although these are estimated values provided for the purposes ofillustration and not limitation. The LAMEE 304 causes water from an airflow (not shown) to be absorbed in the liquid desiccant, resulting inoutput streams 308, 309 having a lower concentration of desiccant,around 20% in this example. Note that the streams 308, 309 are shownexiting the LAMEE 304 separately, however may be joined to a commonfluid port within or outside of the LAMEE 304.

The output stream 308 is fed back into a salinization channel 300 a ofthe first SUPER cell 300 via a fluid junction 310 (e.g., T-junction ormanifold), where it is regenerated to the input concentration. The otheroutput stream 309 is fed into a desalinization channel 300 b of thefirst SUPER cell 300, where it is desalinized to around 10%concentration. This lower concentration solution is divided at fluidjunction 312, which sends a first stream 314 through a desalinizationchannel 302 b of the second SUPER cell 302, resulting in a dischargestream 315 of low concentration, e.g., <1%. A second stream 316 of thelower concentration solution from junction 312 is sent into asalinization channel 302 a of the second SUPER cell 302, where it comesout as an increased concentration stream 318 and is rejoined with LAMEEexit stream 308 at junction 310.

In this example the SUPER cell 302 forms a first stage, and the SUPERcell 300 forms a second stage. The subsequent, second stage produces anoutput stream having a concentration (30% in this example) of the liquiddesiccant higher than the corresponding output stream of previous, firststage output. The corresponding output of the first stage is 20% in thisexample. Pumps 320, 322 are shown driving the flows of liquid desiccant,although the number and location of pumps can vary from what is shownhere. Generally, one pump may be used for each SUPER cell that is usedin a different stage of processing. Other pumps (not shown) may be usedto drive the redox shuttle in the SUPER cells 300, 302.

As with the arrangement shown in FIG. 1 , the system shown in FIG. 3incudes at least one heat transfer element for accepting heat 324 fromthe LAMEE 304 and/or input heat 326 to the SUPER cells 300, 302 and/orfluids pumped through the cells 300, 302. Note that the heat 326 may beapplied to a single stage of the SUPER cells 300, 302 (e.g., cell 300 or302 but not both) where the application of heat will have the greatestimpact on efficiency. This may include applying the heat 326 to just asubcomponent of the single one of the SUPER cells 300, 302. For systemswith more than two stages (e.g., N-stages where N > 2), a subset of thetwo or more stages may be heated, where the subset ranges from one stageto N-1 stages. Any stages not in the subset are not directly heated byheat 326, although some indirect heating may occur due to circulation ofliquid desiccant and the like. The input of heat 326 to the SUPER cells300, 302 can be accomplished in several ways. A hot side of a secondaryheat pump can be brought into thermal contact with the SUPERelectrochemical regenerator cells, such as through conductive heattransfer through the casing, electrodes, membranes, etc.

In FIG. 4 , a block diagram shows a liquid desiccant regeneration systemwith secondary heat pumping according to an example embodiment. A SUPERcell stack 400 includes three cells, each increasing or decreasingsalinity within its channels by about 5% (compared to about 10% in thestack 301 shown in FIG. 3 ). The SUPER cell stack 400 regeneratessolution for a dehumidifying LAMEE 401. As noted above, theelectrochemical regeneration performed by the SUPER stack 400 withcertain desiccants produces a cooling effect. A hot side of a secondaryheat pump includes a heat exchanger 402 that rejects heat to liquiddesiccant flowing through the SUPER stack 400. In this example, thesecondary heat pump is coupled to a primary VC heat pump refrigerantloop, which includes an OA condenser 404, an expansion valve 405, anevaporator 406, and compressor 407. An air conditioning refrigerant, forexample, can be used as a working fluid by both the primary andsecondary heat pump.

The hot side heat exchanger 402 of the secondary heat pump will offsetsome of the cooling effect in the SUPER stack 400. The SUPER stack 400experiences reduced electrical and ionic resistance at highertemperatures leading to reduced losses at higher temperature. The hotside heat exchanger 402 also lowers the hot side temperature of thevapor compression loop before it reaches the condenser 404, which hasdirect thermodynamic benefits for the primary heat pump. The thermalcontact between the SUPER stack 400 and the hot side heat exchanger 402can be achieved via direct integration (e.g., heat conduction to solidcomponents of the stack), indirect integration (e.g., via conductionand/or convective heat transfer to fluid pumped into the stack) or somecombination thereof. This can be accomplished using direct contact tothe refrigerant (which is pumped by the compressor 407) or with a thirdfluid loop (not shown).

It is anticipated that in some cases the SUPER cell stack 400 cannotabsorb all the heat from the secondary heat pump. In other embodiments,the hot side of the heat pump can be coupled (directly or indirectly)with a secondary air contactor, such as humidifying LAMEE 408 whichdesorbs water from a liquid desiccant to an airflow (not shown)resulting in a lowering of temperature of the liquid desiccant. In otherembodiments, the outlet fluid 410 of the SUPER cell stack, which has avery low concentration solution outlet stream, can be reused in thesystem by being fed into the humidifying LAMEE 408, which outputs a moreconcentrated liquid desiccant stream 411. Using the hot side of the heatpump, this outlet fluid 410 could be regenerated even if the ambienthumidity levels were at 100%. This provides unique benefit to theregenerator that the SUPER cell stack 400 would no longer need a drain,in that the outlet fluid 410 would be reconcentrated by the humidifyingLAMEE 408 and be fed back into the SUPER cell stack 400. In cases ofsub-100% humidity, the heat pump would benefit from evaporative coolinglowering the temperature span of the secondary heat pump and increasingits efficiency.

In another embodiment, the dehumidifying LAMEE 401 is brought intothermal contact with the cold side of the heat pump, as indicated byheat exchangers 412 before the expansion valve 405 and the heatexchanger 414 after the expansion valve 405. The amount of coolingprovided could be adjusted, e.g., by utilizing optional variable bypassvalves 415, 416, which in this example, regulate the flow through heatexchanger 414. A similar valve arrangement could be used to regulate theflow through heat exchangers 402, 412 or any other component of thesecondary heat pump. The valves could be linked to a system controllerthat monitors system temperatures and automatically adjusts the valvesto maintain one or more desired operating points.

Cooling of the LAMEE input flow would allow the SUPER cell stack tooperate at lower salt concentrations due to increased RH at lowertemperatures of the LAMEE 401. Lowering salt concentrations wouldincrease the efficiency of the SUPER cell stack 400. Additionally, thesecondary heat pump can directly control outlet temperature in the LAMEEair contactor negating the need for a separate heat exchanger, andpossibly reducing overall system costs. The illustrated evaporator 406provides sensible cooling for the primary airflow, e.g., before or afterpassing through the LAMEE 401.

In FIG. 5 , a block diagram shows a liquid desiccant regeneration systemwith secondary heat pumping according to another example embodiment. Theprimary and secondary heat pump components work similar in this example,however a three-cell SUPER stack 500 feeds multiple stages of liquiddesiccant to a four-stage dehumidification LAMEE 501. In thisarrangement, cold side heat exchangers 512, 514 may have multipleindependent heat exchange sections for each of the differentSUPER-to-LAMEE desiccant flows. This system could use a humidifyingLAMEE to absorb heat as shown in FIG. 5 , as well as control valves toregulate the secondary heat pump.

In some desiccant technologies, the heat pump is used to accept thelatent heat of condensation from the dehumidifier. This is shown in FIG.5 , where outside air plus return air 520 is input to the evaporator 406before being passed through the dehumidifying LAMEE 501 and output aslow RH cooled delivery air 521. The evaporator 406 may need to overcoolthe air sent to the LAMEE 501 to account for the latent heat of liquiddehumidification. The latent heat absorbed in this way is the rejectedto the ambient at the condenser 404. If the liquid desiccant of thedehumidifying LAMEE 501 is kept close to the target temperature of thedelivery air 521, then the air is conditioned on leaving thedehumidifier. This prevents overcooling and lets the conditioningprocess take place at a higher average conditioning temperatureimproving efficiency.

Alternatively, the evaporator can be placed downstream of thedehumidifier. This is shown in FIG. 4 , where outside air plus returnair 420 is input to the dehumidifying LAMEE 401 before being passedthrough the evaporator 406 where it becomes low RH delivery air 421.This configuration eliminates water condensation on the evaporator 406,increasing its efficiency and lowering its air pressure drop, reducingthe fan work of the system. Note that the airflow directions in FIGS. 4and 5 are presented for purposes of illustration, and either embodiment(as well as other embodiments described herein) may use either airflowdirection relative to a dehumidifier and an evaporator.

To operate at the highest possible evaporator temperature and minimizedesiccant system size, a pre-evaporator cooling to the dehumidifier canbe used. In FIG. 6 , a block diagram shows a liquid desiccantregeneration system with pre-evaporator cooling according to an exampleembodiment. A SUPER regenerator stack 600 feeds a dehumidification LAMEE601. A vapor compression heat pump includes an OA condenser 604, anexpansion valve 605, an evaporator 606, a compressor 607, andrefrigerant loop 608. To operate at the highest possible evaporatortemperature and minimize desiccant system size, a pre-evaporator coolingelement can extract heat from the dehumidification LAMEE 601. In FIG. 6, this pre-evaporator and cooling element is shown, for example, by afluid loop 610 and pump 612. The fluid in the fluid loop could be theliquid desiccant, or a different fluid (e.g., water, ethylene glycol,etc.) may be used and transferred to the LAMEE 601 via a heat exchanger.

The evaporator 606 no longer needs to cool below the target outlettemperature but a significant amount of moisture may be removed on theevaporator 606 at no additional energy cost. The dehumidifier 601 canstill be reduced in size due to condensing on the pre-evaporator. If theliquid desiccant regenerator 600 is a SUPER stack, then the dilutesolution can be further diluted by the evaporator condensate, as shownin FIG. 7 . In FIG. 7 , and evaporator 706 and dehumidifier 701 formsingle air contactor that has a first section (the evaporator 706) whichboth cools and condenses to the delivery temperature. The second section(the dehumidifier) performs constant temperature dehumidification. Thetwo sections are in thermal contact using any combination of heat pipes,two-phase flow, single phase flow, conduction, etc. A regenerator 700regenerates the liquid desiccant. If using a SUPER stack for theregenerator 700, than the dilute stream 704 from the regenerator iscombined with condensate at the evaporator 706, resulting in a furtherdiluted output stream 705. This stream 704 could be used to “clean” theevaporator 706 and adds a pressurized outflow from the evaporator 706.Note that certain components of a VC system (e.g., condenser,compressor) would be used with the evaporator 706, but are not shown inthis view. Features shown in FIGS. 6 and 7 (e.g., fluid loop 612 anddilute stream 704) can be added to previously described embodiments inFIGS. 1 and 3-5 .

Note that in the embodiments disclosed above, a heat pump is shown inwith an evaporator that absorbs heat and a condenser that outputs heat.In any of these embodiments, the evaporator can be replaced with achilled solution heat exchanger and/or the condenser can be replacedwith a heated solution heat exchanger. The chilled and heated solutionsmay include water, water/glycol solution, saline solution, etc. The heatpump may still include a vapor compression system with an evaporator andcondenser, but heat transfer is effected through the circulation of thesolution through the system rather than direct contact with theevaporator and condenser.

In FIG. 8 , a flow diagram shows a method according to an exampleembodiment. The method involves producing 800 a first output stream froma first input stream in a liquid desiccant regenerator, the first outputstream having a higher concentration of a liquid desiccant than firstinput stream. A second output stream is produced 801 from a second inputstream. The second output stream has a lower concentration of the liquiddesiccant than a second input stream. An input air stream is exposed 802to the first output stream in an air contactor. The first output streamabsorbs water from the input air stream to form at least one dilutedoutput desiccant stream. The at least one diluted output desiccantstream is circulated 803 back into the liquid desiccant regenerator.Heat is moved 804 from the first output stream before entering the aircontactor to the liquid desiccant regenerator via a heat pump.

In summary, systems and methods are described that can reduce energyconsumption in electrochemically regenerated dehumidification and airconditioning systems, extend system performance, and enable co-locatedsensible heating and cooling with separate control. In one embodiment, asecondary heat pump is used to adjust the operating conditions of anelectrochemically regenerated liquid desiccant system. Anelectrochemically regenerated liquid desiccant dehumidifier has at leastone air contactor for dehumidifying air where a secondary heat pumpsystem is utilized to control the water vapor absorption temperature,the regeneration temperature or a combination of both. The regenerationtemperature can be controlled directly in the regenerator, in one ormore air contactors used for humidification, or a combination of both.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the foregoing specification and attached claimsare approximations that can vary depending upon the desired propertiessought to be obtained by those skilled in the art utilizing theteachings disclosed herein. The use of numerical ranges by endpointsincludes all numbers within that range (e.g., 1 to 5 includes 1, 1.5, 2,2.75, 3, 3.80, 4, and 5) and any range within that range. Alldescriptions of solute concentrations by percentage are meant todescribe percentage by weight unless otherwise indicated.

The foregoing description has been presented for the purposes ofillustration and description. It is not intended to be exhaustive or tolimit the embodiments to the precise form disclosed. Many modificationsand variations are possible in light of the above teachings. Any or allfeatures of the disclosed embodiments can be applied individually or inany combination and are not meant to be limiting, but purelyillustrative. It is intended that the scope of the invention be limitednot with this detailed description, but rather, determined by the claimsappended hereto.

What is claimed is:
 1. A system, comprising: a liquid desiccantregenerator configured to produce: a first output stream from a firstinput stream, the first output stream having a higher concentration of aliquid desiccant than the first input stream; and a second output streamfrom a second input stream, the second output stream having a lowerconcentration of the liquid desiccant than the second input stream; anair contactor coupled to the first output stream and exposing an inputair stream to the first output stream, the first output stream absorbingwater from the input air stream to form at least one diluted outputdesiccant stream, wherein the at least one diluted output desiccantstream is circulated back into the liquid desiccant regenerator; and aheat pump thermally coupled to move the heat from the first outputstream to the liquid desiccant regenerator, the heat moved to the liquiddesiccant regenerator increasing an efficiency of the liquid desiccantregenerator.
 2. The system of claim 1, wherein the heat is moved fromthe first output stream before entering the air contactor or as thefirst output stream enters the air contactor, the movement of heat fromthe first output stream reducing a water vapor absorption temperature ofthe liquid desiccant in the air contactor.
 3. The system of claim 1,wherein the heat is applied to a subset of components of the liquiddesiccant regenerator to cause a temperature gradient inside the of theliquid desiccant regenerator.
 4. The system of claim 1, wherein the heatis applied to a one or more fluid streams inside the liquid desiccantregenerator.
 5. The system of claim 1, wherein the heat pump comprises avapor compression heat pump having a refrigerant loop between acondenser and an evaporator, the evaporator used to cool at least one ofthe input air stream entering the air contactor or a dehumidified outputstream exiting the air contactor, the heat pump further comprising afirst heat exchanger that thermally couples a hot side of therefrigerant loop to the liquid desiccant regenerator and a second heatexchanger that thermally couples a cold side of the refrigerant loop tothe first output stream.
 6. The system of claim 1, wherein the heat pumpcomprises a vapor compression heat pump generating a chilled solutionand a heated solution, the chilled solution being used to cool at leastone of the input air stream entering the air contactor and adehumidified output stream exiting the air contactor, and the heatedsolution being thermally coupled to the liquid desiccant regenerator. 7.The system of claim 5, wherein the evaporator is used to cool thedehumidified output stream exiting the air contactor.
 8. The system ofclaim 5, wherein the evaporator is used to cool the input air streamentering the air contactor.
 9. The system of claim 8, wherein at leastpart of the second output stream is combined with condensate at theevaporator resulting in a further diluted stream being output from theevaporator.
 10. The system of claim 1, further comprising a second aircontactor operable to desorb moisture from a second liquid desiccantstream into a second air stream, the desorbing of the moisture loweringa temperature of the second air contactor, the heat pump being furtherthermally coupled to move part of the heat from the first output streamto the second air contactor.
 11. The system of claim 1, wherein theregenerator comprises two or more stages, each subsequent stage beingconfigured to produce an output stream having a concentration of theliquid desiccant higher than a corresponding output of a previous stage,the first output stream corresponding to the output stream of the two ormore stages having a highest concentration of the liquid desiccant. 12.The system of claim 11, wherein a subset of the two or more stages areheated by the heat pump and any of the two or more stages that are notin the subset are not directly heated by the heat pump.
 13. The systemof claim 1, wherein the liquid desiccant regenerator is driven by anelectric potential that engenders faradaic reactions happening at twodifferent electrodes and a redox material undergoing the faradaicreactions is circulated from one electrode to the other and back again.14. A system, comprising: a liquid desiccant regenerator configured toproduce: a first output stream from a first input stream, the firstoutput stream having a higher concentration of a liquid desiccant thanthe first input stream; and a second output stream from a second inputstream, the second output stream having a lower concentration of theliquid desiccant than the second input stream; an air contactor coupledto the first output stream and exposing an input air stream to the firstoutput stream, the first output stream absorbing water from the inputair stream to form at least one diluted output desiccant stream, whereinthe at least one diluted output desiccant stream is circulated back intothe liquid desiccant regenerator; a vapor compression heat pump having arefrigerant loop between a condenser and an evaporator; and a fluid loopbetween the evaporator and the air contactor, the fluid loop thermallycoupled to move the heat from the air contactor to the evaporator. 15.The system of claim 14, wherein the fluid loop is driven by a pump. 16.A method comprising: producing a first output stream from a first inputstream in a liquid desiccant regenerator, the first output stream havinga higher concentration of a liquid desiccant than the first inputstream; producing a second output stream from a second input stream inthe liquid desiccant regenerator, the second output stream having alower concentration of the liquid desiccant than the second inputstream; exposing an input air stream to the first output stream in anair contactor, the first output stream absorbing water from the inputair stream to form at least one diluted output desiccant stream;circulating the at least one diluted output desiccant stream back intothe liquid desiccant regenerator; and moving heat from the first outputstream to the liquid desiccant regenerator via a heat pump.
 17. Themethod of claim 16, wherein the heat is moved from the first outputstream before entering the air contactor or as the first output streamenters the air contactor, wherein moving the heat from the first outputstream reduces a water vapor absorption temperature of the liquiddesiccant in the air contactor.
 18. The method of claim 16, wherein theheat pump comprises a vapor compression heat pump having a refrigerantloop between a condenser and an evaporator, the evaporator used to coolat least one of the input air stream or a dehumidified output streamexiting the air contactor, the heat pump further comprising a first heatexchanger that thermally couples a hot side of the refrigerant loop tothe liquid desiccant regenerator and a second heat exchanger thatthermally couples a cold side of the refrigerant loop to the firstoutput stream.
 19. The method of claim 18, further comprising combiningat least part of the second output stream with condensate at theevaporator resulting in a further diluted stream being output from theevaporator.
 20. The method of claim 16, further comprising: desorbingmoisture from a second liquid desiccant stream into a second air streamat a second air contactor, the desorbing of the moisture lowering atemperature of the second air contactor; and moving part of the heatfrom the first output stream to the second air contactor via the heatpump.
 21. The method of claim 16, wherein the regenerator comprises twoor more stages, each subsequent stage being configured to produce anoutput stream having a concentration of the liquid desiccant higher thana corresponding output of a previous stage, the first output streamcorresponding to the output stream of the two or more stages having ahighest concentration of the liquid desiccant.
 22. The method of claim16, wherein the liquid desiccant regenerator is driven by an electricpotential that engenders faradaic reactions happening at two differentelectrodes and a redox material undergoing the faradaic reactions iscirculated from one electrode to the other and back again.